“Emissions” refer to the introduction of chemicals, particulate matter, or biological materials into the atmosphere, ground, or water system that potentially can cause harm or discomfort to humans or other living organisms, or may damage the natural environment.
GHG is a collective term for gases such as carbon dioxide, methane, HFCs, SF6, and nitrous oxide that trap heat in the atmosphere and contribute to climate change. GHG accounting and reporting is the discipline of tracking GHGs produced as a result of executing business processes, including manufacturing, travel, keeping of livestock, etc.
The term “carbon dioxide equivalent” (CO2e) is a common normalized unit of measurement, such as expressed in tonnes of CO2e, that is used to compare the relative climate impact of the different GHGs. The CO2e quantity of any GHG is the amount of carbon dioxide that would produce the equivalent global warming potential. There are publicly accepted factors that are used to convert an entity's emissions, usage of resources (e.g., electricity, gas, oil, coal, etc.), or waste products, among other things, into a CO2e emission.
An organization, such as a company or other entity, may want to, or be required to, reduce their CO2e emissions. For example, a company's CO2e emissions per year, either overall or for targeted activities, may be capped by a governmental or industrial organization.
Although an organization can measure or calculate the CO2e emissions directly generated by the organization, such as by direct physical measurement or multiplying its own kwh or gas usage by an accepted conversion factor, the organization is not able to determine the CO2e emissions that are generated by its suppliers of goods and services as a direct consequence of the organization. Such information would be valuable to a socially conscience organization concerned with reducing CO2e on a global scale.